Including that overnight tragedy on Everest involving at least 12 guides. The guides had gone early to fix ropes for climbers before the dangerous and deadly avalanche hit right above base camp. ABC's David Kerley is here with all of the details. Good morning, David. Reporter: Good morning, robin. We know that Everest is extremely dangerous. Steep and deep canyons of ice. But this was an avalanche that swept down at an unexpected time of day. That avalanche swept down Mt. Everest early in the morning, killing at least 12 and leaving at least 3 missing, as rescue crews searched frantically for any survivors. The victim, all sherpas. The legendary local master mountaineers who come from Nepal. They had gone up to fix ropes, setting the ropes for the hundreds of climbers who were gathered at base camp. The climbers were going to scale the mountain in about a month when the weather conditions are more favorable. Gavin turner was watching at base camp when the avalanche happened. The experience was going well. And then, suddenly, there was a huge thud. We got covered by this enormous cloud of snow and snow dust. For a few seconds, I thought, wow. Reporter: The avalanche happened right under camp 2, on the area of the mountain known as the popcorn field. It's 21,000 feet. Allen Arnett reached the summit of Mt. Everest back in 2011. The sherpas are more at risk because how off they are going through the ice wall in this particular area. Reporter: Gavin, from Australia, who saw the avalanche, tells us that the sherpas are the backbone of the efforts of climbers to get to the summit. Gavin says he's going to contemplate whether he stays on the mountain and makes an attempt at the top of the world in light of what happened this morning.

This transcript has been automatically generated and may not be 100% accurate.

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